FNB hard lock on account

I changed the date of my credit card auto payment (from the 24th to the 31st) after it had gone off for the month. Including the auto payment (under R 3 000) just over R 42 000 was paid into the account since the 24th of the month. However, after changing the date, FNB's systems recalculate the payment due for the month and ignore all payments made. So now my account is locked and I'm told that even though I've paid over 10 the required amount over the last week of the month, according to FNB I didn't make the required payment and my account is locked. Calling the call centre all I'm told is that I haven't made the payment and now my account is in bad standing.

This is ridiculous. If that is how the system works then they should at least inform you when you make the change.